Method of utilizing magnesian rock in the preparation of calcium-magnesium bisulphite liquor in towers



I 5-45; through whichblow-ofl' gas fromthe 'diges- Patented; 0a. 20, i931 ME rnonoF n'iirLIzING MAGNESTAN Rock In This PREPARATION on CALCIUIVLMA GQ-j W ,n sIUmBIsUIrHITE LIQUQR N TOWERS aration of nor in towers.

' a Bis'ulphite liquors'usedinjthe' cooking of.

wood chips in the manufacture "of sulphite pulp consist of sulphurous acid and either calcium bisulphit'e "or mixed calcium 1 and magnesium bisulphite.- jj" Numerous advantages have been claimed byfdiflerent operators for the use of the mixed liquors of calcium and magnesium bisulphites over'theistraight calciumliquor. Of-these the chief are the better yield I and-higher quality 1 5 f pulp produced; the feasibility of treating numerous kinds of wood which cannot be satisfactorily Cooked with calcium bisulphitealone, the lower consumption of sulph'ur,the. reduction or; elimination of [calc1um'mon-o 'Zflsulphite and calcium sulphate from the pulp, V

and thereduced necessity forcarry'i'ng a high content of free sulphurous acid. In spite'of these advantages the use of magnesium bisulphite has in recent years decreased con- 1 @225 siderably, due to the greater cost of ,aration. The method herein described has ther'el ore" been "devised as a means of prepar ing cheaply and efiiciently bisulphite liquors containing calcium and magnesium salts-of 336 any desired'ratio withinratherwide.- limits.

base of the last; tower of the series and is 7 then usually fortified 'in; sulphur dioxide in another tower filled with" inert material,

tersi'spassed. r t a In some plants-dolomite magnesium}con- I taining rock is usedfor the purpose .of;in-n

corporating magnesiain the'bisulp-hite liquor.

50; Wherethis is done additional .tofwer capacity;

' This intention relates to a method of utili zg ing magnesium containing rock in the prep-i calcium-magnesium bisulPhite'liqg the gas. top of thetank and euenly ldistributediover v the first compartment 'byany; I

the surface of its prep t 1 in the tower is The 'bisulphitesolut-ion'jis' taken from the 1928. Serial No; 280,957. is required, for. reasons which will be given ,laterr" I i- :Liquors containing both calcium and'inagr1 nesium bi'sulphitesare at present usually :pree' paredby the milk-of lime system. Calcinektl. dolomite or magnesium containing limestone is used as the base, and a slurryof milk oflime is prepared by'slaking the calcine in Water. The absorption apparatusconsists of a tall multiple-compartment tank, the u er three orfour compartments forming'tthe rel J I action chambers; The compartments areseparate'd :by perforated partitions and the bbt-' tom section of the] tank is ,fille'd-Twithtile" blocks to give a large'absoi'ption surface for The 'milk of limef is' fed=in=at the,-

suitable means. j Sulphur dioxid'e gas is in troduced at the bottom of th'e' tank, at; which; point, the acid isdrawn ofl; :Inthesolu'tion of" nmimt WALLA E; sewa e-, ,onorrawn, awman,

the calc'ine insoluble-calcium .monosulphi-te; and soluble magnesium monosulphiteare I formed,along w1th sulphurousacid', and-this i mixture passes into lower tanks whereth solution is fortified in sulphur dioxide and j the monosulphites are converted to *bi'sul phites Off calcium and magnesium, both of which are soluble, I i 3 The operating cost a nd the cost of raw ma ,terial are both higher in the 'milk-ofJime-th'anf pense' justified onlybyxthe compensating advantages of the use of mixed ,l-iquor'.{ J IIt is'a well; known fact" that limestone is uble 'th'an magnesite. In actualftrial it has beenfound that limestoneis about nine times stone @will have to be provided,.in=order to I '95 effected in practice by'using largerltower's or secure sulfici'ent time for solution. This' i s more of them in series Moreover, the rock ystem, and theadditional eX.-

wer,very considerably in v r used contains any two of the-mineralslime-y I,

stone,dolomite-and:magnesite in thedissemi- Y Y v I 100, r I

nated form in which'theyusually occur, the i a moresoluble than dolomite and still more solt the tower and milk-of-lime systems without the limitations of the former or the disadvan tages of the latter A .furtherobjectof the invention is to provide'for definite control of the lime-magnesia ratio in sulphite'liquor produced by the tower system, regardless of the character of the rock with which the tower is filled. 7 I

1 Theinvention thus comprises the calciu tion of magnesium containing rock which is then preferably reduced to a fine state of division and introduced in regulated quantities l into the top of the towersusually employed in the tower system- Calcination ofthe magnesium containing rock isan important step in this process, since containedmagnesia and lime. When properly calcined these bases dissolve more rapidly even than limestone. To secure maximum solubility the calcination should be carried out at a comparatively ifis'preferably between800and' 1000 deg. C.

' since when calcined at a high temperature the contained magnesia becomes less active chemically; One may use any reasonably pure rock conta ning magnesium carbonate or magne- :9 sium and calcium carbonates in the desired proportions, for all decompose readily within the temperature range given. i H

The next step (which if preferred maybe omitted) is the reduction ofthel calcine to a fine state of divisionl Iffthis is to be efiected by'grinding alone such operation will normally take place at the calcination plant, before shipment. The calcine is comparatively soft, and is therefore readily pulverized. If it is to be disintegrated by slalring alone, or by a'combined slaking and crushing operation, this will ordinarily be carried out at the sulphite plant itself. f 5

. In the preferred method the resultant fines, either dry'or wet, are agitated with sufficient water, to give'a thin slurry and this slurry is fed ata controlled rate into the water stream passing to the head of the tower, which is filled with coarse limestone or dolomite, as in theusual tower process. If desired, the fine calcine may be fed directly to the tower, in a dry state,'to be carried downby the water supply. It-is evident thata very close control of the "amount of calcine admitted to the tower can be obtained. In the tower the finely 'fine calcine is added it greatly increases the rate of solution of the low temperaturef.

divided calcine containing lime and magnesia, eitherfas oxides or hydroxides, will be rapidly dissolved, due to its ready solubility and to its large surface exposure, which for the same weight of material, will be many thousands of times the area of the large pieces of coarse rock in the tower. I r

If coarse calcine be used it may be added to the towerin any convenient way. Its rate of solution iscbviously lower than that of fine calcine,fbut. it is nevertheless considerably.

higher than that of limestone.

It is evident thatif sufficient calcine be-added much more base will be dissolvedin a given time and only one tower will be required to supply, without undue loss of sulphur dioxideyall the combined tual trial it has been to satisfy the sulphur dioxide present very little lime'stonegoes into solution. 'In consequence the composition of the solution can be varied from straight calcium bi sulphite to approximately that ofthe mixed bisulphites in the ratio in which the magnesia and lime occur 1n the calcine.

To further illustrate this point the results j A five-foot v of the following tests are given. glass tower 1 in diameterwas filled with commercial limestone about in size.

Sulphur dioxide gas was introduced at. the

bottom and water at the top. Fine calcined magnesium containing rock containing Ca() 23% and MgO 72% was, added tothe water feed and samples the base; The following table illustrates the effect of additionsof calcine.

. v I Ratio, No calcine added 7 200.00 2 gm. calcine added every 20 minutes 1.37 2 gm. calcine added every 15 minutes 41.00 2 gm, calcine added every 5'minutes V 0.64

In every tion, and in the last instance very. little limestone was dissolved, over half of the lime being derived from the magnesium containing rock.

It is obvious proposed process present tower equipment will require but slight modifications and additions. In new installations the cost of these changes will be more than offset by the saving resulting from the reduction in tow-' er capacity. It will thus be apparent that, in addition toachieving the objects above set forth, the process of thisinvention has veryimportant secondary advantages, which may be summarized'as follows: v V

'1. The quantity of calcine fed can be readily varied, thus permitting the combinedacid content of the liquor to be readily maintained, even in cold weather.

2. The numberor size of towers required can'be considerably reduced. 7

acid necessary. In ac-' found that if sufficient of liquor were collected at case all the calcine went into soluthat for the adoption of s) already been expelled in calcination. The smaller volume of gases will obviously move at a lower velocity, affording additional time; for the absorption of sulphur dioxide. It is also evident that the smaller volume of gases will carry less sulphur dioxide out of y the tower.

What I claim and Letters Patent is:

1. A method for the utilization of mag nesium containing rock in the preparation of magnesium-calcium, bisulphite liquors in towers which comprises calcining the magnesium containing rock, feeding the calcine and water to the top of a tower and passing sulphur dioxide through said tower countercurrent to said water and calcine to react with the latter. H 2. A method for the utilization of magnesium containing rock in the preparation of magnesiumcalcium bisulphite liquors in desire to secure by towerswhich comprises calcining the magnesium containing rock, reducing the calcine to a fine state of division, feeding the fine calcine and water to the top of a tower and passing sulphur dioxide through said tower countercurrent to said water and calcine to re+ U f act with the latter.

3. A method for theutilization of magnesium containing rock in the preparation of magnesium-calcium bisulphite liquors in towers whlch comprises calcining the magnesium containing rock at a temperature between 800 and 1000 deg. 0., reducing the cal-. cine to a fine state of division, feeding the 1 fine calcine and water to the top of a tower and passing sulphur dioxide through said tower countercurrent to said water andcalcine to react with the latter. p

4. A method for the utilization of magnesium containing rock in the preparation of magneslum-calcium bisulphite liquors in towers which comprises calcining thev magnesium containing rock, reducing the calcine to a fine state of division byv slaking with water, feeding the fine calcine and water to the top I of a tower and passing sulphur dioxide through said tower countercurrent to -said water and calcine to react with the latter.

5. A method for the utilization of'mag nesium containing rock in the preparation towers which comprises calcining the magof magnesium-calcium bisulphite liquors in with the substitution of calcine for raw rock, due to the fact that the carbon dioxide has passing sulphur dioxide through said tower countercurrent to said water and calcine to 4 react with the latter.

6. A method for the utilization of mag- 'nesium containing rock in the preparation of magnesium-calcium bisulphite liquors in nesium containing rock, reducing the calcine to a fine state of division, feeding the fine calcine as a slurry into the water supply g0- ing to the top of a tower and passing sulphur dioxide upwardly through said tower to react with said calcine. j

7. A method for utilization of magnesium containingrock in the preparation of bisulphite liquors in towers which comprises towers which comprises calcining the mag- I calcining the magnesium containing rock, V

reducing the calcined rock to a fine state of division, introducing the calcined rock into} i the top of a tower through which sulphur dioxide and water flow in counter current relation, and controlling the combined-acid f content of the liquor by regulating only the quantity of calcined magnesia rock introduced to the tower.

' In testimony whereof I have afiixed m signature.

DANIEL ALLACE STEWART.

- nesium containing rock, reducing the calcine I 

